In an effort to promote world peace, fast-food chain Burger King suggested putting its rivalry with McDonald’s on hold for just one day. But the idea didn’t fly with the execs from McDonald’s.

Burger King extended an olive branch to McDonald’s, its longtime competitor, in the form of a pretty unique proposal: Create a hybrid burger that contains the ingredients from each company’s signature burger, and sell it at a pop-up restaurant in Atlanta on World Peace Day. Proceeds would then go to an organization that promotes world peace.

Whether it’s a genuine offer or a marketing gimmick is up for debate, but Burger King went right ahead and created a website that contains an open letter to Mcdonald’s, a potential recipe for the hybrid burger that will be named the McWhopper, and even the reason behind holding it in Atlanta (it’s the midway point between McDonald’s and Burger King’s headquarters in Chicago and Miami, respectively).

There are also mock-ups of the hybrid uniforms that employees will don and packaging for the burgers. Burger King also took out full-page advertisements in The New York Times and Chicago Tribune to get the attention of McDonald’s.

But McDonald’s was less than impressed. In a Facebook post by its CEO Steve Easterbrook, the proposal was harshly shot down, with Easterbrook adding that “a simple phone call will do next time” in his postscript.

The post has garnered plenty of negative comments, with some saying that McDonald’s missed out on an opportunity to do good. No idea what Burger King will do to salvage the situation, but it was fun while it lasted.